[NEXT-696] New middleware slows down routing in production

Verify canary release

• I verified that the issue exists in the latest Next.js canary release

Provide environment information

Operating System:
Platform: win32
Arch: x64
Version: Windows 10 Pro
Binaries:
Node: 16.14.2
npm: N/A
Yarn: N/A
pnpm: N/A
Relevant packages:
next: 12.2.0
eslint-config-next: 12.2.0
react: 18.2.0
react-dom: 18.2.0

What browser are you using? (if relevant)

Chrome 103.0.5060.66

How are you deploying your application? (if relevant)

next start

Describe the Bug

New middleware slows down on routing in production (dev is okay), example code that slows down:

import { NextResponse } from 'next/server';

const Middleware = (req) => {
  /** To lower case redirect. */
  if (req.nextUrl.pathname === req.nextUrl.pathname.toLowerCase())
    return NextResponse.next();

  return NextResponse.redirect(new URL(req.nextUrl.origin + req.nextUrl.pathname.toLowerCase()));
};

export default Middleware;

Expected Behavior

Work as expected with no slow down, with previous _middleware.js there was no problem

To Reproduce

Create middleware.js file under root folder and use code from example

_NEXT-696

Start with the root-level middleware.js reproduction and run it in production with next start, comparing the behavior against the previous _middleware.js setup. Investigate the production routing slowdown described by the example, and consider the issue done when production routing no longer regresses while the lowercase redirect still works.